A technology of transmitting data via a ring-type communication system that is formed in a ring shape by using a technology such as Ethernet (registered trademark) is known. The data means a frame in the Ethernet. In the ring-type communication system, in order to make it possible to maintain data transmission even at a time of occurrence of a failure, a redundancy is provided for a data transmission path. Further, for a technology to recover from a failure in the ring-type communication system, it is demanded that an interruption time in which data transmission is not available be reduced, without requiring an operator's work.
As the technology to recover from a failure, a technology to transfer (transmit) failure detection information at a time of failure detection, and a technology to set and cancel a blocking state in the ring-shape communication system are known. Further, as a technology to recover from a failure for the ring-type communication system, a ring-protection method according to ITU-T (International Telecommunication Union Telecommunication Standardization Sector) recommendation G.8032 is known. The ring-protection method is a method specialized for the ring-type communication system, and is a method that is a technology to recover from a failure at higher speed than STP (Spanning Tree Protocol). Frames that are targets of protection according to the ring-protection method are used in communications without establishing a connection.
The ring-type communication system employing the ring-protection method has, as will be described with reference to FIG. 26A, a master node (referred to as MN in the figures) N1. A blocking port BP is set to the master node N1 for avoiding a loop of data.
In the ring-type communication system, when a failure 101 occurs between a node N5 and a node N4 for example, the node N5 and the node N4 transmit failure notification messages 102, as depicted in FIG. 26B. When receiving the failure notification messages 102, the master node N1 opens the blocking port BP. Thus, the ring-type communication system provides redundancy such that, even at a time of an occurrence of a failure, the communications can be continued.
As depicted in FIG. 26C, when a recovery is made from the failure 101, the node N4 and the node N5 transmit recovery notification messages 103. When receiving the recovery notification messages 103, the master node N1 sets the blocking port BP again as depicted in FIG. 26D, and transmits, to the other nodes N2 through N6, re-setting notification messages. It is noted that, with reference to FIGS. 26A through 26D, description has been made assuming that the number of nodes is 6, as N1 through N6. However, the ring-type communication system may be such that the number of nodes is equal to or more than 6, or less than 6.
Japanese Laid-Open Patent Applications Nos. 2004-147172 and 2007-174119, and “http://www.itu.int/rec/T-REC-G.8032” disclose related art.